In medicine, an embolism occurs when an object (the embolus, plural emboli) migrates from one part of the body (through circulation) and causes a blockage of a blood vessel in another part of the body. Blood clots form a common embolic material. Other possible embolic materials include fat globules (a fat embolism), air bubbles (an air embolism), septic emboli (containing pus and bacteria), or amniotic fluid. Emboli often have more serious consequences when they occur in the so-called “end-circulation” areas of the body that have no redundant blood supply, such as the brain, heart, and lungs. Assuming normal circulation, a thrombus or other embolus formed in a systemic vein will always impact in the lungs, after passing through the right side of the heart. This forms a pulmonary embolism that can be a complication of deep-vein thrombosis.
Embolism can be contrasted with a “thrombus” which is the formation of a clot within a blood vessel, rather than being carried from elsewhere. Thrombus, or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e., clotting factors). A thrombus is physiologic in cases of injury, but pathologic in case of thrombosis. A thrombus in a large blood vessel will decrease blood flow through that vessel. In a small blood vessel, blood flow may be completely cut-off resulting in the death of tissue supplied by that vessel. If a thrombus dislodges and becomes free-floating, it becomes an embolus.
Some of the conditions in which blood clots develop include atrial fibrillation (a form of cardiac arrhythmia), heart valve replacement, a recent heart attack, extended periods of inactivity (see deep venous thrombosis), and genetic or disease-related deficiencies in the blood's clotting abilities.
Preventing blood clots reduces the risk of stroke, heart attack and pulmonary embolism. Heparin and warfarin are often used to inhibit the formation and growth of existing blood clots, thereby allowing the body to shrink and dissolve the blood clots through normal methods (see anticoagulant). Regulating fluid flow through catheters can help minimize embolism and health risks associated therewith.